1. Field of the Invention
The invention relates to an image forming apparatus of an electrophotographic printing method or an electrostatic recording method such as, for example, a copying machine, a printer or a facsimile apparatus, and particularly to an image forming apparatus in which a toner on an image bearing member is electrostatically removed.
2. Description of Related Art
In recent years, as a plural-color or full-color image forming apparatus adopting an electrophotographic printing method, there has been proposed an image forming apparatus of a so-called intermediate transfer type in which toner images of respective colors formed on an image bearing member such as a photosensitive drum are successively superposed one upon another on an intermediate transfer member to thereby form a color image thereon, and the color image is collectively transferred to a recording material.
In such intermediate transfer type, a toner image is formed on the photosensitive drum by charging means, exposing means and developing means disposed around the photosensitive drum. Then, the toner image on the photosensitive drum is electrostatically transferred to an intermediate transfer member such as an intermediate transfer belt in a primary transfer portion by transferring means. Also, yellow, magenta, cyan and black toner images can be successively transferred to the intermediate transfer member to thereby form a full-color image on the intermediate transfer member.
The toner image transferred to the intermediate transfer member is carried to a secondary transfer portion by the rotation of the intermediate transfer member, and is electrostatically transferred to a recording material. As a method of removing any toner not transferred to the recording material at this time but residual on the intermediate transfer member (untransferred residual toner), there is a method of urging a cleaning blade against the intermediate transfer member to thereby remove the residual toner. There has also been proposed a method of applying a bias to a cleaning member to thereby electrostatically remove the residual toner.
The method of electrostatically removing the toner is advantageous to such a problem as the influence upon the life of the intermediate transfer member which poses a problem when the toner is removed by blade cleaning means, or the fluctuation of a load by the fluctuation of frictional resistance.
Here, as regards the charging polarity of the untransferred residual toner after secondary transfer, there are the toner charged to the positive polarity and the toner charged to the negative polarity.
So, two cleaning members are used to collect both of the untransferred residual toner charged to the positive polarity and the untransferred residual toner charged to the negative polarity to thereby sufficiently remove the untransferred residual toner.
Biases of different polarities are applied to the two cleaning members. That is, a bias of the positive polarity is applied to one of the two cleaning members, and a bias of the negative polarity is applied to the other cleaning member. In this manner, the untransferred residual toner after the secondary transfer is sufficiently removed. However, there has arisen the problem that even if as described above, two cleaning members are provided and biases of different polarities are applied to these two cleaning members, when image formation is continuedly effected, the untransferred residual toner after the secondary transfer becomes incapable of being sufficiently collected.